High-potential electrical apparatus



Jan.V 18, 1927.*l l '1,614,762

J; A. PRocToR HIGH POTENTIAL ELECTRICAL APPARATUS Filed Dec. 12. 1925 3 Sheets-Sheet l MCP INVENTOR Jo-Iz n, erfrocor ATTORNEY Jan. 1s, 1927.

J. A. PROCTCR HIGH` POTENTIAL ELECTRICAL APPARATUS Filed-Dec. L2. 1923 5 Sheets-Sheet INVENTOR Jhn nflerfmcor ATTORNEY Jan. l18 1927. 1,614,762

J. A. PROCTOR HIGH POTENTIAL ELECTRICAL APPARATUS Filed Dec. 1,2,y 1923 3 Sheets-Sheet 3 NVENTOR ATTORNEY Patented Jan. 18, 1927.

UNITED STATES JOHN A. PROCTOR, OF LEXI TGr'lOwl', IiIASSACHUSE'I'TS,

PATENT OFFICE.

l TO WIRELESS SPE- 0F NEW YORK.

HIGH-POTENTIAL ELECTRICAL APPARATUS.

Application filed December 12'. 1323.

This invention relates to improvements in electrical devices such as condensers and transformers, especially those. involving high potential differences between different parts of the device, and more especially those also operated at high frequencies as in radio communication.

The object of the invention is to reduce heating of high potential. .insulating material employed, and thereby prevent deterioration or destruction' of such insulation.

The invention consists of the arrangements which are illustrated in the drawings (which are about one-half scale) and described in the text, by way of example, in a present-day commercial high potential mica condenser, especially in those adapted for nigh frequency service.

Fig. 1 is a central vertical section of an embodiment of the invention showing the differences from Fig'. 5 which involve the application of the invention to the condenser of Fig. 5.

F ig. 2 is a central vertical section of a slightly different design of condenser, and showingl the embodiment therewith of a slightly modified -form of the invention.

Fig. 3 is a similar view of the same design of condenser as that of Fig. 2, but illustrating a modified embodiment of the invention therewith.

Fig. is a horizontal section at t3- G of Fig. 2 to illustrate in plan the general design of the condenser stacks of Figs. 2 and 3.

Fig. 5 is a diagram illustrating certain electrical actions in the condenser of the prior art, as contrasted with the electrical actions of the invention as shown in Figi'. 6.

F 6 is a diagram illustratingv the different electrical action in the condensers of Figs. l-l which results from the embodiment of the invention with the condenscrs of Fig. 5.

The prior art condenser illustrated in Fig. 5 may assume various different forms, as in the case of Figs. Ld and G to which the invention is shown as applied. The condenser of Fig. 5, however, is shown because it illustrates a present standard commercial form of mica condenser like l-1l or 6 save for the present invention. The arrangement of the pair of stacks in Fig. l. is known as the mid-point ar'ra `ement wherein the high potential ends of the two stacks are brought Serial No. 680,121.

together' in the central part of metal casing MC against a metal block M1 in which is secured the high potential stud U at MP. The outer ends of the double stack are electrically and mechanically connected to the sides of the metal casing by way of metal compression plates MCP and screws lV, these outer ends being at low potential and they and the metal casing` constituting the low potential terminal of the condenser. Preferably the stacks within rthe metal casing are embedded in a paraliin wax filler X. This preferably is effected after assembly of the condenser by inverting the assembly, lacking metal bottom plate MB, and introducing the molten wax in connection with suitable vacuum treatment; after which the bottom plate MP is screwed for permanent assembly with the casing. r The upper part of the casing is formed with an opening to permit passage of high potential stud U. Across this opening there was placed, in the prior art condensers (Fig. 5), a thin mica disk MD1 to close the opening and exclude foreign matter and to retain the wax in the casing, also to insulate high potential stud U from the low potential metal casing. Disk MD1 was secured to the metal casing MG by a metal ring MR1 (Fig. 5) screwed to the casing as shown and thereby electrically constituting a part of the casing. Above disk l\ID1 and around high potential stud U was mounted an insulator I1, consisting of a built-up and processed stack of mica sheets. Below disk MD1 was a similar insulator I2, (Fig. 5), both insulators I1 and I2 having been intended to insulate high potential. stud U from low potential metal casing MC, including metal ring MB1; said insulators also having been intended to prevent creepage from the high potential stud U to the low potential parts of the apparatus. Supported on top of insulator I1 was (as there yet is permissively and preferably) a metal disk or bell7 B, (Fig. l) serving, among other things, as an electrode of a safety spark-gap between itself and metal retaining ring MB1 of Figxb or MR2 of iig. l.. The capacity between B and MB1 is adjusted by means of one or more shims SP, to about 1.4- times the rated voltage of the condenser. Prior to the present invention, the bell or disk B was designed with the further obj-ect of establishing an electrostatic field between B and ring MR1, (Fig. 5), in order to shunt such field from insulator' I1, thereby to avoid heating of and injury to the latter. While it is believed that such action took place, and successfully accomplished its purpose at voltages up to certain igh values, yet certainly it was not adequate to prevent the heating of the high potential insulating material around stud Il at yet higher potentials as 50,000 volts more or less, at radio frequencies. The operation of the condenser otherwise was entirely satisfactory, but under very high duty the heating of the insulating material I1, MD1 and I2, (Fig. 5), was so great as to be serious in causing electrical losses which injured and sometimes destroyed the insulation. I concluded, therefore, that the electrical action taking place might be such as illustrated by the dash lines in Fig. 5, i. e., that notwithstanding the provision of metal disk B of Fig. l, most of the electrostatic field established between high potential stud U, on the one hand, and metal ring MR1 (Fig. 5) and metal casing MC at low potential, on the other hand, passed directly between such parts, as shown by electrostatic lines ESL, Fig. 5, and therefore through insulation I1 and I2, thereby causing excessive heating of such insulation, I1, I2 and MD1, such insulation being a poor dielectric as compared with air.

Proceeding on that hypothesis. I modified the condenser of Fig. 5 to the form shown in Fig. 5 wherein the chief differences are the elimination of the insulation I1 and I2 of Fig. 5, the substitution for such insulation of the metal parts Y and Z, and the modification of metal ring MR1 to the form of ring MR2 shown in Fig. l. The only insulating' material left was mica disk MD2. which was not changed from disk MD1 ot' Fig. 5, save that the disk MD1 in Fig. 5 is one thirty-second of an inch in thickness and the disk MR2 of Fig. l was reduced to fifteen thousandths inch in thickness, with a view of reducing the thickness or vertical length of the insulating material to the lowest degree consistent with the function of the disk as a cover for the casing to hold the wax X or other insulating filler, as oil, inside the metal casing MC.

The object of the above changes in Fig. l was to determine whether the heating of the insulating material could be reduced so far as not to result in injury to it, and consequently to avoid electrical losses. I believed that the action which would result in Fig. l would be that illustrated in Fig. 6 where the electrostatic lines ESL pass chiefly from metal parts Y and Z to the low potential structure, without passing to any serious extent through the mica disk insulator MD2. The space between metal part Y and metal ring MRs of Fig. 6 is an air space which constitutes a perfect dielectric medium. The space between metal part Z and casing MC is filled with wax X which is not seriously injured by heating, although (Fig. lower insulator I2 was so injured.

Tests of the arrangement of Fig. 1., under the same condition-s which resulted in excessive heating of insulators I1 and I2 of Fig. 5, resu ted in mica disk MD2 of Fig. l running cool, thereby tending to prove my hypothesis shown in Figs. 5 and 6 and certainly demonstrating that my changes in Fig. l resulted in avoiding excessive heating of the high potential insulating material, and that perfect operating conditions resulted not-withstanding` the substitution of the metal parts Y and Z of Fig. l for the insulating` material I1 and I2 of Fig. 5.

The effect of the arrangement in Fig. 1 is to localize the electrostatic field away from insulator MD2, and to eliminate it, or at least greatly reduce it. in the space occupied by the insulator itself. This localization, however, is eidected in places much closer to the insulator` than disk B. Preferably, as shown, metal parts Y and Z, which are substituted for the insulators I1, I2 of Fig. 5. are located directly adjacent mica disk HD2; but at locations progressively remote from the disk their surfaces are extended nearer to the metal casing parts, so that at a location notfar from the disk MD2 there is provided a gap (between Y and MR2) which is substantially shorter than the distance at the insulating disk MD2 between the metal casing parts Y, ll and the high potential parts. Preferably. also, the metal ring- MR2 has a similarly formed surface, i. e.. from its portion adjacent the insulating disk MD2 the surface of MR2 gradually approaches the high potential upper metal member Y, so that the shortest gap between MR2 and Y is established comparatively close to the mica disk. Beyond this gap. across which the most intense field is established, the surfaces of metal member Y (and Z) preferably are curved in a direction opposite to their curvature upon leaving the mica disk MD2; and preferably the same is true of the inner surface of ring MR2; for the purpose in both instances of avoidingr sharp electrode points.

Functions of insulator' I1 of Fig. were to support disk B (Fig. l) adjustably by shim or shims SP. and to increase mechanical rigidity of stud U; and metal member Y of Fig'. l, substituted for said insulator I2. takes up said functions, but preferably an additional metal member SP2 is interposed between member Y and shims SP for the following purpose. In Fig. l. disk D yet serves as an electrode for the safety gap or static shield between itself and ring MR2. In fact, disk B is adjusted so that the annular gap between it and ring MR2 is adjusted 'than -is upper member Y.

or-luminum. So tar as concerns the shunt- 'ing of 'the electrostatic field from the insulating material, (as MD), the eiiective portionsof ring MR2 and members Y and Z are simply their proximate conducting surfaces, electrically connected respectively with the high and low potential parts of the apparat-us.

The intensity of the electrostatic field between the high and low potential conducting parts is a function of the operating voltage and lfrequency. Ibelieve that the heat-- ing of the insulating material in the old form of Fig. 5 was due to the presence of the insulators F, I2 as imperfect dielectrics lying in the intense radial iields between the -high'potential stud U and the low potential metal vcasing MC. I believe that the presence of such imperfect Adielectric resulted in substantial power losses which were sufricient in higher voltages and frequencies to cause the undue heating of the insulating` material which resulted in its subsequent disintegration. My invention provides tor the employment of a minimum amount of undesirable dielectric in the path of the intense electrostatic field (as only thin disk MD, Fig. v.5, or MD2, Fig. l), and in a path between member Y `and ring MR2 (Fig. l) which'is entirely through air for the sub-- staiitial or most intense portion ot' the electrostatic tield.

Fig. l shows the lower metal member Z yas located further from the metal casing The object ot this is to provide a lower capacity through wax X inside the casing than through the fair vgap between Y .and MR2 outside the casing. This in turn is for the purpose ot reducing Athe losses through `the wax which otherwise would be greater than those vthrough the perfect dielectric. air.

In Fig. 2 is shown another standard form of high potential series sectional sheet stach; condenser, and a modilied form of clamping ring. Here such ring. MK3, is shown as a sheet metal member, stamped or spun to shape, and strong enough to clamp mica disl: MD2 to the main part MC ot the metal casing,-such thin sheet metal member serving for the invention inasmuch as its conducting surface is the prime electrical functioning part. The condenser stack arrangement shown in Fig. 2 is similar to the type of Fig. l, save that here four stacks are employed, Sl-S (see horizontal section,

Fig. 4), the four high potential ends of these stacks abutting against a massive heatabsorbing metal block M2 in which the high potential stud ll is secured as shown. The metal stan'iping MK3 oit Fig. 2 may be applied to any other appa atus having conducting parts oit high potential (litter-ence and located comparatively close together.

In Fig. 3 is shown a standard condense).` ot the type ot Fig. 2, and in horizontal section in Fig. el.; and to this are applied modified 'iorn'is ot metal members Y and Z which have been substituted for insulators Il, l2 or" 5. The part Z in Fig. 3 is formed hollow, to provide all necessary service vfor establishing the intense electrostatic field shunting mica disk MD2. The upper metal member Y is shown in a torm where, above its shortest distance from sheet metal ring MRS, it does not curve away from said ring but entends upwardly in a straight line 4a. sutlicient distance to avoid establishment ot electrostatic field relations between the metal ring and an edge or pointed surface ot' member Y.

ln Fig. 3 also the members Y and Z are shown in extended heat-conducting contact with one another. lin Figs. l-Q, a central portion ot the mica covering disk was cut away only su'liiciently to permit passage of stud U. ln Fig. 3, however, a larger central opening is toi-med through t-he mica dish, and in this opening the members Y and Z are permitted to come in contact with one another, and at their outer edges they clamp the mica dislr or collar between them at its inner perifery. Below metal nut N screwed on stud U to support members Z, Y and B are placed metal rings SP4t around stud U for the purpose of increasing heat conduction from metallic mass M2 up through nut N, stud U and metal members Z and Y to disk B, the latter serving as a heat radiator ot extended surface. As shown, disk B has extended heat-conducting suritace contact with metal member Y. This arrangement serves the double purpose ot ccncentrating the intense lield in shunt to mica disk MD'i and also in conduct-ing heat from the interior o'if the condenser. This all illustrates a` high duty condenser, the stack portion ot which is divided into four portions as shown for the purpose oi absorbing heat rapidly into central metallic mass M2. The above arrangement around stud U above metallic mass serves to conduct away said absorbed heat to heat-radiating member B. lit desired yet further to increase the heat connuction ot the parts around stud U, lower metal. member Z may be formed solid as in Figs. l and 2. Such adequate heatconducting and radiating means serves to prevent melting ot' wax lV inside the casing due to heating of the stack, and thereby prevents disintegration 'of the wax which otherwise might result in electrical breakdown of the vital parts of the condenser. Metal members Y and Z ot Figs. l-3, substituted ter the insulating material I1, I2 of Fig. 5, provide a much larger` thermal path trom the condenser stacks.

liv/'bile the use ot' metal for the casing of electrical apparatus, and 'for the condensers illustrated, is preferred tor various reasons,

" yet the case itself could be oi insulating material; and the invention is not limited to an instance where the casing is ot conduct` ing material. Irrespect-ive ot the material of the casing, and whether or not it were conducting, the apparatus might have two terminal leads insulated from one another and extending from the interior to the eX- terior oi' the casing. In such instances, two of the iield-shunting complete assemblies oi Fig. l would be employed, one tor each insulated terminal lead. In tact, thatis the case in the standard condenser illustrated in Fig. l, where the drawing shows only onehalt` oi the condenser, the metal easing MC containing two pairs ot stacks like the pairs shown in Fig. l, each pair having its midpoint high potential member M1 connected to a high potential stud U provided with the arrangements including the mica disk and the rest ot the parts in the upper portion ot Fig. l, the casing being provided with two separate openings, one for each of the two hich potential studs.

Shunting the electrostatic iield away from the insulating disk MD2 reduces the liability to creepage along the disk between the high and low potential parts; that is, the substantial removal of the tield from the disk reduces the electrostatic strains to which the disk is subjected. In substituting the metal members Y and Z oi' Fig. l for the insu laters Il, I2 ot 5, it might have been thought that it would be necessary to increase the length ot extension of the mica disk MD2 between the high and lo poten tial parts. But I found that that was not necessary, and it may be that such lack oi necessity is due to the reduction ot creepage along the disk which accompanied the shunting oi' the electrostatic ield away from the disk. In the use of insulators Ii, I2 shown in Fig. 5, itwas considered necessary to guard against creepage by the provision ot' the staggered path illustrated in the lower insulator I2. The ei'i'ectiveness of the new means tor shunting the iield is thus indicated notwithstandingr the total elimination ot insulators Il, or Fig. 5.

In Figs. l-S, the space between ring lill 2 and central metal member Y is arranged to be somewhat greater than the distance at which the condenser will break down under test or operating conditions. This arrangement is t'or the purpose of obtaining as intense an eletrostatic field through the perfect dielectric, air, at this location as is possible without danger oi breakdown.

It is desirable to have the distances between high potential stud U and lower potential parts as large as is practical, irrespective of the spacing between ring MR2 and central metal member Y; that being for the purpose or reducing the inherent capacity between the stud and the low potential parts through any torni of imperfect dielectric material necessary to be used between the high and low potential parts, such as the mica disk HD2. But such dimensions of the disk are limited by practical considerations,

and it the diameter of the disk could be very greatly increased l etween the high and low potential parts, the invention would be less necessary to reduce heating. In the special case illustrated in the drawings, the design of the metal casing, having a reduced upper portion approaching the top opening, is such as to permit a covering insulator MD2 of small diameter which permits its use in the i'iorm oi'l a thin mica disk. In this form, the upper part oit the casing1 below the mica disk, approaches toward central stud U to a distance approximating the general location of ring MR2 relative to the stud U. I-Ience, in this form, it is preferable to substitute lower metal member Z i'or lower insulator I2 ot Fig. 5, in addition to substituting metal member Y l) tor upper insulator' .l of Fig. 5; because iii this substitution were not made the closeness of the upper part of the metal casing to central stud U would cause heating in lower insulator I2 of Fig'. :3, or even heating of mica. disk MD2 if lower insulator I2 of Fig. 5 were omitted and no metal part Z of Fig. l substituted.

Y Lower metal member Z is located a greater distance from the low potential parts than is upper metal member Y. Disk B is adjusted by shims Si? so that its annular rim is located closer to the part oitl metal ring MR2 than the distance between said rin@r MR2 and upper metal member Y c The employment of adjustable electrode B for the safety spark-gap, in conjunction with the means below it for shunting the electrostatic iield from the insulating cover HD2, is very desirable. Tilhile it is possible to space upper metal member Y from ring MR2 so as lto provide a safety gap between them, in addition to shunting the field away trom the mica disk, yetit is extremely desirablc to have the saiety gap adjustable, and at present it seems impracticable to provide an adjustable gap between members Y and IYIR2.

The invention is not limited in its application to series-sectional stacks which are divided up into separate physical portions, as shown. Such forms are shown because they permit rapid heat dissipation and because heat is likely to be generated in the Sti stack itself in condensers designed for such service as to require the use of the invention to reduce heating of the insulating member.

As indicated above` the invention is operative between conducting surfaces of the two parts having a high potential ditl'erence between them. Fundamentally` therefore, it consists in providing an arrangement of such conducting surfaces which are respectively electrically connected to the high and low potential terminals. Broadly speaking, the recise manner of arrangement of such surfiices is less material than the tact of the arrangement itself, and the provision of the surfaces shown on the metal members Y, Z and MR2 are those which now seem most practical and convenient for use in connection with the standard type of condenser to which the invention thus far has been applied. The substitution of the metal members Y, Z for the insulators Il, I2 of Fig. 5 is, in effect, a reduction of the thickness of the insulating material in a direction at right angles to the shortest line connecting theI two conducting parts of high potential difference, andi a location of metal members Y, Z quite close to said shortest line connecting the conducting parts.

The covering insulator MD2 may be of any desirable insulating material and may have substantially kgreater thicknem than is shown but the object of the invention in reducing its heating will be eifected in proportion as its thickness is comparatively small. It the material of this insulating cover is suiiiciently strong or its thickness sufficiently great, or both, it may serve as a compression member to compress the stack against the bottom of casing MC in an instance when the stack is arranged at right angles to the stacks shown in the drawings. In condensers embodying the invention, there may be many variations, t-he only thing invariable being that there is a high potential difference between two neighboring conducting parts of the apparatus. The heating of insulation which the invetnion prevents is a result of the small over-all volume of the apparatus in proportion to the great potential difterence between the two upper conducting parts, and it is such small over-all volume which causes the neighboring relation of the parts which results in heating of insulation in the lack ofthe invention. The reasonffor the arrangement of series-sectional sheet-stack is that such an organization results in a potential difference which is high in proportion to the space occupied by the stack. Various methods and means may be employed to clamp the stack, in lieu of the clamping arrangement shown. For example, if desired, the stack may be held under compression by a clamping means independent of the casing but supported within the casing. If the metal casing have straight vertical sides, as distinguished from the curved upper portion shown in the drawings, the lower metal member Z of Figs. 143 may be omitted. owing lto the consequent increased separat-ion between 'the part of stud U below mica disk MD2, on the one hand, and the nearest part ofthe side walls ot the casing, on the other hand.

I particularly point out and distinctly claim the part, improvement, or combination which I claim as my invention or discovery, as ollows1 n l. The improvement in electrical sheet condensers oi' the type having a stack of series-connected sections and therefore having a high potential diference across the electrical ends of the stack, and having av metal casing enclosing such stack, connected to a low potential part of the stack and having an opening for a terminal lead 'from a high potential portion of such stack, which lead lies in the neightborhood .of a part of the metal casing, and an insulating member covering said opening and through which the terminal lead extends; the improvement comprising means for reducing the heating oit the insulating member and consisting of metal members surroundin the high potential lead on both sides o the insulating member and adjacent thereto, saidy members being electrically connected to said high potential lead and having outer surfaces located at points substantially close to the insulating member, and substantially closer to the low potential metal enclosingcasing than is the high potential terminal lead'at its portion which extends through the insulating member.

2. The improvement on high potential electrical condensers of the ty e having a metal enclosing casing for te `stack of sheets, the casing being provided with an opening for a high potentiallead from the stack, said lead lying in the of a part of the meta-l casing, an lnsulating member covering said opening, said high potential terminal lead extending through the covering insulator, said improvement consisting of metal members electrically connected with the high potential terminal-lead and having outer surfaces located at points substantially close to the covering insulator, and substantially closer to the metalcasing than is the high potential terminal-lead at its portion which extends through the covering insulator, said metal members being used in place of the insulating members hereto-I fore employed around` the high potential lead and respectively above and below the covering insulator.

3t In a sheet-stack condenser of the" type comprising a metal casing enclosing the high potential sheet-stack, electrically connected to an electrical end'of the stack, to constitute one terminal of the condenser, and llavneighborhoodl ing an opening through which extends a lead connected to another electrical end of the stack which lead is located in the neighborhood of a part of the casing; said casing and lead being of high potential difference and lying sufficiently close together to establish an intense electrostatic field between them; and a cover of insulating material for said opening and extending between said lead and casing-terminal, through which cover said lead extends, said insulating cover being of comparatively slight thickness in the direction of extent of said terminal but lying in the normal path of said field; said lead and casing-terminal being provided with substantially extensive conducting surfaces which, at their portions substantialljv close but not adjacent to insulating cover, lie closer to one another than they do at their portions adjacent the insulating cover.

el. In an electrical aupa atus housed in a l l metal casing having a hgh pitential lead extending out through an opening in the casing and in the nei borhood of a part of the casing.7 said ca and lead being of high potential diii'eience and lying sunlcientljfv close together to establish an intense electrostatic held between them; the combination with an insulat coter for said opening and extending weon the high potential lead and the metal casing and in the normal path of said field, said insulating cover being of slight thickness in the direction of extension ol" the high potential lead; ot metallic means n'iounted ad" cent the high potential lead and the insulating` cover and having a substantially extensive surface which at a location substantialljfY close to the insulating cover but not adjacent thereto lies closer to the metal casing than it does at a location adjacent to the insulating cover.

5. The improver ent in reducing the heating of insulating material lying in electrical apparatus between neighboring conducting parts of high potential difference and located sutlicienlly close together to establish an intense electrostatic field between them which consists in the substitution for a part of the longitudinal dimension of the insulating material, of a member ha a substanti ally extensive conducting race connected to one of the conducting parts. said surface at a location substantiallf.'v close but not adjacent to the remaining insulating material being located substantialljv7 closer to the other conducting part than tie Condireting surface and said other conducting part are located to one another adjacent the remaining insulating` material itself.

6. ln an electrical apparatus having neighboring conducting parts of high potential difference and lying sulhciently close together to establish an intense electrostatic field between them and insulating material rampes between them in the normal path of such field, the means for reducing the heating of the insulating material which consists of an arrangement of substantiallav extensive sur- -faces of said conducting parts wherein they ing material than it does adjacent the insu.

lating material itself.

8, ln a high potential electrical apparatus of the type having a grounded metal casing enclosing an insulating yfiller surrounding the electrical apparatus itself` said casing having an opening for a terminal lead and insulating material between the casing and terminal lead at the casing-opening, the improvement consisting of the provision of" metal surfaces of the casing and terminal lead ljlg .jacent the insulating material and respectivel7 inside and outside the casing, said surfaces outside the casing being separated from one another at a location close to said insulating material by an air space shorter than the distance between the casing and terminal lead at the insulating material at the casing-opening; and said surfaces inside the casing being separated from one another by a portion of the insulating liller of shorter length than the distance between the casing and terminal lead at the insulating material at the casing-open ing, said surfaces inside the casing being separated a greater distance from one another than the separation of said surfaces outside the casing 'from one another.

9. ln a high potential electrical apparatus of the type having a grounded metal enclosing casing having an opening for a terminal lead, said casing and lead being at high potential difference and suticientlj7 close together to establish an intense electrostatic field between them and insulating m'aterial between the lead and casing at the casing-opening and located in the normal path of such held. the improvement consisting of the provision of substantiallj7 eXtcn sive metal surfaces of the casing` and terminal lead lying outside of the casing and adjacent the insulating material and extending beyond the latter said surfaces being separated from one another by an air space and lying closer to one another ata location such field, the improvement lill close ybut not adjacent to the insulating material than they do at the kinsulating material itself.

10. Ina high potential electrical apparatus oi the type having a grounded metal casing enclosing an insulatingr filler surrounding the electrical apparatus itself, said casing having an opening for a terminal lead and insulating material between the lead and casing at the casing-opening, the improvement consisting of the provision of metal surfaces of the casing and terminal lead, which surfaces lie adjacent the insulating material and inside the casing, said surfaces being separated from one another by the insulating filler and lying closer to one another at a location close but not adjacent to the insulating material than they do at the insulating material itself.

1l. In an electrical apparatus having neighboring conducting parts of high potential difference and located sufficiently close together to establish an intense electrostatic field between them and an insulating men ber between them and located in the normal path of such field. the means for reducing heating of the insulating member by such field, which consists of comparatively slight thickness of such member and an arrangement of substantially extensive surfaces of said conducting parts to lie nearer to one another close to but not adjacent said insulating member than they do at the insulating member itself.

12. In an electrical apparatus having neighboring conducting parts of high potential difference and lying sufficiently close together to establish an intense electrostatic field between them, and having an insulator extending between them and located in the normal path of such field, the improved means for substantially shunting said field from said insulator` which comprises two metal surfaces of substantial extent and electrically connected with said conducting parts of high potential difference` and having portions located adjacent said insulator and close to the shortest line between said conducting parts, and also having portions substantially close to but not adjacent said insulator; said metal surfaces lying closer to one another at their portions close to but not adjacent the insulator than they do at their portions adjacent the insulator, establishing between their said more closely related portions a gap constituting'a path, in shunt to and substantially close to the insulator', for the intense electrostatic field between said conducting parts of high potential difference.

13. In an electrical apparatus having neighboring conducting parts of high potential difference establishing an intense static field between them, and having an insulator in the normal path of said field,

close to but not adjacent the insulator` located closer to the second conducting part than,is its portion adjacent the insulator. and constituting a field-shunting device; and said second surface having a range of adjustable mounting within a shorter distance from the first conducting part than the shortest distance between said first conducting part and the second surface, and constituting a safety gap.

l-i. In an electrical apparatus having neighboring conducting parts of high potential difference, and insulating material between them of comparatively slight thickness in the direction at right angles to the shortest line between said conducting parts, and means for reducing heating of said insulating material which comprises the relatiifc arrangen'ient of surfaces of said conducting parts wherein such surfaces lio nearer to one another close to the insulating member than they.'Y do at the insulating member itself, such surfaces curving away from one another on both sides of their portions which lie nearest together.

l5. In an electrical apparatus having neighboring conducting parts of high potential difference and an insulating member between them of comparatively slight thickness in a direction at right angles to the shortest line between the two conducting parts, two mutually neighboring surfaces of the respective conducting parts located close to said insulating member being arranged to lie closer to one another than do the portions of the respective conducting parts at the insulating member itself; and two other mutually neighboring surfaces of the conducting parts located more remote from the insulating member than said first two surfaces, being arranged to form a vsafety gap by lying more closely together than said first two surfaces.

16. In a high potential sheet-stack condenser having a metal enclosing casing connected to a low potential part of the stack, said casing having an opening for a terminal lead from a high potential part of the stack, the combination with an insulating disk covering said casing opening and surrounding said high potential lead, and a metal ring as a part of the casing and holding said disk thereto; of a metal disk surroundingl the high potential lead outside the casing and spaced from said metal ring to establish a safety gap; and metallic means between said metal disk and said insulating disk and adjacent the latter, said metallic means and metal ring being shaped externally relative to one. another to establish between them an air A Lp near the insulating;` disk Which is longer than said saitet),v gap but shorter than the dish ance at the insulating disk between the high potential lead and the metal casing'.

17. In a high potential electrical apparatus ot the type having a grounded metal enclosing casing having an opening for a terminal lead, and insulating` material between the lead and casingl at the opening, said insulating` material being short in the direction of extent of the terminal lead, the improvement consistingl of the arrangement of the surface ot a portion of the casingl to lie closer to the terminal lead at a location near the insulatingl material than the casinand terminal lead lie to one another at the insulating material itself.

18. In a series-sectional sheet-stack condenser ot the type having a staek-enclosing met-al casing` formed with an opening 'tor a terminal lead from the stack, and an insulatiner disk closing the opening, the improvement consisting ot the )revision oit a metal member adjacent the insulatingv disk and outside the casing in contact with atmospheric air, said metal member being in thermal and electrical connection 'ith the terminal lead and formed with a surta e which at a location near the insulating,` disk is separated a less distance from the casing :han the dimension ot the insulating disk between the terminal lead and the casing.

19. In a series-sectional sheet-stack c0ndenser ot the type having a stack-enclosing metal casing formed With an opening for a terminal lead from the stack, and an insulating member of comliaratively small thickness closingv the opening and located between the terminal lead and the casing and through which insulating member the terminal lead cwends, the improvement in the construction et the terminal lead outside the casing and in atmospheric air which comprises a sui-tace ot large heat-radiating area, a portion oi' which close to the insulating member is arranged to lie closer to the metal casing than it dees directl)7 at the insulating membei'.

ser oit the type having a stack-enclosing al casing, termed with an opening for e 'minal lead from the stack, and an insulatinl collar between the terminal lead and casing' at said opening and through which the terminal lead extends, the improvement consisting in the provision of two metal members around the terminal lead, one inside and one outside the casing and adjacent the insulating collar and clamping it between them, said metal members being in heat-conducting Contact with one another at the inside of the insulating collar and each having an outer surface which at a portion close to the insulating collar is closer to the metal casing than is each metal member directlvv at the insulating collar.

JOHN A. PROCTOR. 

